Various devices and techniques have been developed for occluding aneurysms or other vascular deformations. A common type of aneurysm treatment utilizes a detachable coil that is fed into the aneurysm to substantially occupy the aneurysm volume. The typical approach for implanting an embolic coil in an aneurysm involves attaching the coil to the distal end of a pushwire, and introducing the pushwire and coil through a catheter lumen until the coil is pushed into the aneurysm. The typical manner of detaching the coil from the pushwire involves using a direct current to cause electrolysis of a sacrificial joint between the pushwire and the coil. The coil can then serve to mechanically occlude a significant volume of the aneurysm and thereby reduce blood circulation within the aneurysm. After a period of time ranging from several hours to several weeks, the volume of the aneurysm can become fully occluded as blood clots about the coil. Eventually, the aneurysm will be reduced and reabsorbed by the body's natural wound healing process. This type of vaso-occlusion system was disclosed by Guglielmi in U.S. Pat. Nos. 5,122,136 and 5,354,295.
Another manner of treating an aneurysm was disclosed by Guglielmi (see U.S. Pat. Nos. 5,976,131; 5,851,206) and is described as electrothrombosis. In this particular approach, a catheter and pushwire are used to push a wire coil into the aneurysm that is connected to an electrical source. The system then delivers radiofrequency (Rf) current to the coil which is adapted to heat the blood volume within the aneurysm to cause thermal formation of thrombus (see U.S. Pat. No. 5,851,206; Col. 5, line 5). The conductive coil disclosed by Guglielmi in U.S. Pat. No. 5,976,131 has an insulated tip or other arrangements of insulation around the coil to prevent localized “hot spots” (see U.S. Pat. No. 5,976,131; Col. 3, line 53).
It is believed that several risk factors are involved in any uncontrolled use of significant levels of Rf energy to cause so-called electrothrombosis. Most important, the use of electrical energy to cause current flow between a coil (first electrode) within an aneurysm and a ground (a second body electrode) will likely cause high energy densities and highly localized heating of tissue that comes into contact with the coil. If the wall of the aneurysm contacts the energized portion of a coil, there is a significant danger of perforation or ablation of the aneurysm wall that could be life-threatening. Further, the use of uncontrolled energy delivery to an implanted coil could heat adjacent brain tissue to excessive levels resulting in loss of brain function or even death. For these reasons, the coils disclosed by Guglielmi were provided with an insulating material covering the tip of the coil that is most likely to come into contact the wall of the aneurysm. However, it is still likely that unwanted localized heating will occur within the aneurysm sac when attempting to cause ohmic heating of the blood volume in an aneurysm by creating Rf current flow between an electrode coil and a body electrode.
Another disadvantage of using the typical commercially available wire coil is that the physician must estimate dimensions and volume of the aneurysm and then feed multiple coils into the aneurysm. The deployment of each coil is time consuming, and the detachment of the coil from the introducer pushwire also is time consuming.